1. Field of the Invention
The present invention relates to an improved trailer coupling construction for use in securing a trailer to a tractor having a fifth wheel and, more specifically, it relates to such a construction which provides effective antifriction properties.
2. Description of the Prior Art
In connection with tractor-trailer combinations, it has been known to provide a fifth wheel member on the power providing or tractor portion of the assembly. The fifth wheel construction generally consists of a steel plate having an opening which is adapted to receive a portion of the trailer coupling. The undersurface of a forward portion of the trailer generally has a steel plate secured to it with a downwardly depending king pin which is received within the opening of the fifth wheel. In this manner, the two vehicles are mechanically joined so that the tractor may pull the trailer while permitting the desired relative rotational movement. In moving such a vehicle, in order to minimize resistance to relative rotational movement between the contacting metal plates of the fifth wheel and tractor coupling, it has been known to provide lubrication such as a grease therebetween. One of the problems of such an approach has been the fact that the grease is effective for only a certain period of time and the further problem that the grease tends to entrap dirt particles which interfere with relative free rotational movement between the fifth wheel and the trailer coupling.
U S. Pat. No. 4,457,531 discloses the use of a Teflon (Polytetrafluoroethylene) layer on the tractor plate in cooperation with the steel plate 7 which is secured to the king pin of the trailer and is removable therefrom in order that the plate may be removed from the trailer when the tractor is to be coupled to other trailers. See also U.S. Pat. No. 3,218,989 which relates to use of an annular wear band and liner retainer for use in railway car truck bolsters.
U.S. Pat. No. 3,275,390 discloses securement of a self-lubricating material which may be polyethylene or polypropylene to a trailer body by means of a self-locking retainer ring. One problem with such construction is the risk of the ring breaking and causing dangerous conditions on the road.
U.S. Pat. No. 3,337,277 discloses the use of a layer of Polytetrafluoroethylene containing filler material such as fiberglas and carbon to increase the compressive strength of the material. Apertures pass through both the veneer and the plate. As the king pin has a fixed length increasing the thickness of the plate and veneer will interfere with securement of the fifth wheel to the trailer unless the king pin is enlarged.
U.S. Pat. No. 4,121,853 discloses the use of a sandwich containing a pair of metal plates between which a Teflon disk is inserted in a fifth wheel bearing attachment. The construction perpetuates contact between the metal undersurface of the trailer bearing element and the fifth wheel with the Teflon layer being said to carry the load and minimize frictional rubbing between the fifth wheel plate and the undersurface of the trailer.
It will be appreciated, therefore, that while the use of antifriction materials in lieu of grease has been suggested in the prior art, there remains a very real and substantial need for improved attachment means for trailer plates and improved materials for reducing friction and wear within such an environment.